This invention relates generally to the use of electric impulses to increase the permeability of cancer cell walls, and, more specifically to providing access of anticancer drugs directly into the cancer cell cytosol.
The effectiveness of many anticancer drugs is limited by the inability of the drug to penetrate the cancer cell membrane. Although the dosage of the drug may be increased in order for the drug to have its desired effect on the target cell, such increases in dosages often result in the death of host cells. The need exists, therefore, for a method of introducing cancer drugs into the target cancer cell while at the same time minimizing the death of healthy host cells.
The present invention solves this problem through a technique known as "electrochemotherapy." Electrochemotherapy, involves the application of electric pulses to a target cell resulting in the increased permeability of the cell membrane. This increased permeability by electric pulses, known as "electroporation," allows a greater number of the anticancer drug molecules to enter the target cell's membrane. This further allows a much lower concentration of the drug to be introduced without sacrificing efficacy and at the same time reducing or eliminating conventional side effects.
The use of electrical impulses on the biological membrane has been generally known. Techniques such as electroporation and electrofusion have been utilized in many areas of the biomedical sciences. Electrofusion is a process by which membrane fusion can be induced by exposure to electrical fields. Electrofusion has many practical applications such as the formation of hybridomas, the production of monoclonal antibodies, the study of membrane fusion mechanisms, and the examination of cytosolic events. In addition, electrofusion has proved to be a valuable tool in examining membrane interaction between two cells or within a single cell. Materials can also be introduced into cells by utilizing liposomes encapsulated with the selected material and then fusing with the recipient cells. Additionally, individual cells can be incorporated into intact tissue in a process known as cell-tissue electrofusion.
Electroporation techniques have also been used in a variety of situations for a variety of purposes. For example, electroporation has been used to transfect genetic material into target cells (Titomirov et al., Biochimica et Biophysica Acta, 1088:131-134 (1991)). In addition, studies of the effects of high-voltage electrical impulses with an anticancer drug on an in vivo growing malignant tumor has been studied (Okino, Jpn. J. Cancer Res., 78:1319-1321 (1987)). However, this technique required the penetration of the host organism's skin tissue in order to directly apply the electrical impulses. Furthermore, previous techniques have resulted in widespread destruction of host cells thus neutralizing any added benefit of the lower dosage rates of the anticancer drug (See discussion, Weaver et al., U.S. Pat. No. 5,019,034)). Only one attempt to combine bleomycin and electric pulses in vivo has been reported (Okino et al., Jpn. J. Cancer Res. 78:1319-1321 (1987)). Mohri and Okino obtained partial regression (PR) of AH-109A hepatocellular carcinoma in Donryu rats after the combined administration of bleomycin and one exponentially decaying intense (5000 V/cm, 2 ms) pulse. However, these conditions produced oedema even in the absence of drug and caused necrosis of the surrounding skin when used in combination with bleomycin.